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LTM8050MPY

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24
LTM8050
13
8050fc
For more information www.linear.com/LTM8050
APPLICATIONS INFORMATION
Table 1: Recommended Component Values and Configuration (T
A
= 25°C)
V
IN
RANGE V
OUT
V
BIAS
C
IN
C
OUT
R
FB
f
OPTIMAL
R
T(OPTIMAL)
f
MAX
R
T(MIN)
3.6V to 58V 0.8V 2.8V to 25V
3× 4.7µF, 2220, 100V 3× 220µF, 1206, 4V
Open 110kHz 392k 125kHz 340k
3.6V to 58V 1V 2.8V to 25V
3× 4.7µF, 2220, 100V 3× 220µF, 1206, 4V
1.87M 110kHz 392k 125kHz 340k
3.6V to 58V 1.2V 2.8V to 25V
2× 4.7µF, 2220, 100V 3× 220µF, 1206, 4V
953k 125kHz 340k 150kHz 280k
3.6V to 58V 1.5V 2.8V to 25V
2× 4.7µF, 2220, 100V 2× 220µF, 1206, 4V
549k 150kHz 280k 180kHz 232k
3.6V to 58V 1.8V 2.8V to 25V
2× 4.7µF, 2220, 100V 2× 220µF, 1206, 4V
383k 180kHz 232k 215kHz 191k
4.1V to 58V 2.5V 2.8V to 25V 4.7µF, 2220, 100V 220µF, 1206, 4V 226k 230kHz 174k 270kHz 150k
5.3V to 58V 3.3V AUX 4.7µF, 2220, 100V 220µF, 1206, 4V 154k 280kHz 140k 330kHz 118k
7.5V to 58V 5V AUX 4.7µF, 2220, 100V 100µF, 1210, 6.3V 93.1k 400kHz 93.1k 460kHz 80.6k
10.5V to 58V 8V AUX 4.7µF, 2220, 100V 47µF, 1210, 10V 54.9k 550kHz 64.9k 690kHz 49.9k
17V to 58V 12V AUX 4.7µF, 2220, 100V 22µF, 1210, 16V 34.8k 600kHz 57.6k 750kHz 44.2k
24V to 58V 18V 2.8V to 25V 4.7µF, 2220, 100V 22µF, 1812, 25V 22.6k 760kHz 42.2k 850kHz 37.4k
34V to
58V 24V
2.8V to 25V 4.7µF, 2220, 100V 22µF, 1812, 25V 16.5k 900kHz 33.2k 960kHz 30.1k
9V to 24V 0.8V V
IN
4.7µF, 1206, 25V
2× 220µF, 1206, 4V
Open 150kHz 280k 300kHz 130k
9V to 24V 1V V
IN
4.7µF, 1206, 25V
2× 220µF, 1206, 4V
1.87M 180kHz 232k 345kHz 113k
9V to 24V 1.2V V
IN
4.7µF, 1206, 25V
2× 220µF, 1206, 4V
953k 230kHz 174k 400kHz 93.1k
9V to 24V 1.5V V
IN
4.7µF, 1206, 25V 220µF, 1206, 4V 549k 280kHz 140k 460kHz 80.6k
9V to 24V 1.8V V
IN
4.7µF, 1206, 25V 220µF, 1206, 4V 383k 330kHz 118k 500kHz 73.2k
9V to 24V 2.5V V
IN
4.7µF, 1206, 25V 100µF, 1210, 6.3V 226k 345kHz 113k 600kHz 57.6k
9V to 24V 3.3V AUX 4.7µF, 1206, 25V 100µF, 1210, 6.3V 154k 425kHz 88.7k 650kHz 52.3k
9V to 24V 5V AUX 4.7µF, 1206, 25V 47µF, 1210, 10V 93.1k 500kHz 73.2k 700kHz 48.7k
10.5V to 24V 8V AUX 4.7µF, 1206, 25V 47µF, 1210, 10V 54.9k 600kHz 57.6k 750kHz 44.2k
17V to 24V 12V AUX 2.2µF, 1206, 50V 22µF, 1210, 16V 34.8k 760kHz 42.2k 850kHz 36.5k
18V to 36V 0.8V 2.8V to 25V 1µF, 1206, 50V
3× 220µF, 1206, 4V
Open 100kHz 432k 200kHz 205k
18V to 36V 1V 2.8V to 25V 1µF, 1206, 50V
3× 220µF, 1206, 4V
1.87M 120kHz 357k 250kHz 162k
18V to 36V 1.2V 2.8V to 25V 1µF, 1206, 50V
2× 220µF, 1206, 4V
953k 140kHz
301k 270kHz 150k
18V to 36V 1.5V 2.8V to 25V 1µF, 1206, 50V
2× 220µF, 1206, 4V
549k 180kHz 232k 300kHz 130k
18V to 36V 1.8V 2.8V to 25V 1µF, 1206, 50V 220µF, 1206, 4V 383k 220kHz 187k 350kHz 110k
18V to 36V 2.5V 2.8V to 25V 1µF, 1206, 50V 100µF, 1210, 6.3V 226k 300kHz 130k 425kHz 88.7k
18V to 36V 3.3V AUX 1µF, 1206, 50V 100µF, 1210, 6.3V 154k 345kHz 113k 550kHz 64.9k
18V to 36V 5V AUX 1µF, 1206, 50V 47µF, 1210, 10V 93.1k 425kHz 88.7k 800kHz 38.3k
18V to 36V 8V AUX 2.2µF, 1206, 50V 22µF, 1210, 16V 54.9k 550kHz 64.9k 1.03MHz 25.5k
18V to 36V 12V AUX 2.2µF, 1206, 50V 22µF, 1210, 16V 34.8k 760kHz 42.2k 1.03MHz 25.5k
24V to 36V 18V 2.8V to 25V 2.2µF, 1206, 50V 22µF, 1812, 25V 22.6k 800kHz 38.3k 1.03MHz 25.5k
18V to 58V 0.8V 2.8V to 25V 1µF, 1206, 100V
3× 220µF, 1206, 4V
Open 100kHz 432k 125kHz 340k
18V to 58V 1V 2.8V to 25V 1µF, 1206, 100V
3× 220µF, 1206, 4V
1.87M 100kHz 432k 125kHz 340k
18V to 58V 1.2V 2.8V to 25V 1µF, 1206, 100V
3× 220µF, 1206, 4V
953k 100kHz 432k 150kHz 280k
18V to 58V 1.5V 2.8V to 25V 1µF, 1206, 100V
2× 220µF, 1206, 4V
549k 110kHz 392k 180kHz 232k
18V to 58V 1.8V 2.8V to 25V 1µF, 1206, 100
V
2×
220µF, 1206, 4V
383k 125kHz 340k 215kHz 191k
18V to 58V 2.5V 2.8V to 25V 1µF, 1206, 100V 220µF, 1206, 4V 226k 180kHz 232k 270kHz 150k
18V to 58V 3.3V AUX 1µF, 1206, 100V 100µF, 1210, 6.3V 154k 280kHz 140k 330kHz 118k
18V to 58V 5V AUX 1µF, 1206, 100V 100µF, 1210, 6.3V 93.1k 400kHz 93.1k 460kHz 80.6k
18V to 58V 8V AUX 2.2µF, 1206, 100V 47µF, 1210, 10V 54.9k 550kHz 64.9k 690kHz 49.9k
18V to 58V 12V AUX 2.2µF, 1206, 100V 22µF, 1210, 16V 34.8k 600kHz 57.6k 960kHz 30.1k
2.5V to 54.7V –3.3V AUX
2× 4.7µF, 2220, 100V
100µF, 1210, 6.3V 154k 300kHz 130k 330kHz 118k
3.3V to 53V –5V AUX 4.7µF, 2220, 100V 100µF, 1210, 6.3V 93.1k 400kHz 93.1k 460kHz 80.6k
3.3V to 50V –8V AUX 4.7µF, 2220, 100V 47µF, 1210, 10V 54.9k 550kHz 64.9k 690kHz 49.9k
4.5V to 46V –12V AUX 4.7µF, 2220, 100V 47µF, 1210, 16V 34.8k 600kHz 57.6k 750kHz 44.2k
6V to 40V –18V 2.8V to 25V 4.7µF, 2220, 100V 22µF, 1812, 25V 22.6k 760kHz 42.2k 850kHz 37.4k
10V to 34V –24V 2.8V to 25V 4.7µF, 2220, 100V 22µF, 1812, 25V 16.5k 900kHz 33.2k 960kHz 30.1k
Note: Do not allow V
IN
+ BIAS to exceed 72V.
LTM8050
14
8050fc
For more information www.linear.com/LTM8050
APPLICATIONS INFORMATION
Table 2. Switching Frequency vs R
T
Value
SWITCHING FREQUENCY (MHz) R
T
VALUE (kΩ)
0.1 432
0.2 215
0.3 137
0.4 93.1
0.5 73.2
0.6 57.6
0.7 51.1
0.8 38.3
0.9 33.2
1 32.4
1.2 24.9
1.4 20
1.6 16.2
1.8 14
2 11
2.2 8.06
2.4 7.15
Operating Frequency Trade-offs
It is recommended that the user apply the optimal R
T
value given in Table 1 for the input and output operating
condition. System level or other considerations, however,
may necessitate another operating frequency. While the
LTM8050 is flexible enough to accommodate a wide range
of operating frequencies, a haphazardly chosen one may
result in undesirable operation under certain operating or
fault conditions. A frequency that is too high can reduce
efficiency, generate excessive heat or even damage the
LTM8050 if the output is overloaded or short circuited. A
frequency that is too low can result in a final design that has
too much output ripple or too large of an output capacitor.
BIAS Pin Considerations
The BIAS pin is used to provide drive power for the internal
power switching stage and operate other internal circuitry.
For proper operation, it must be powered by at least 2.8V. If
the output voltage is programmed to 2.8V or higher, BIAS
may be simply tied to AUX. If V
OUT
is less than 2.8V, BIAS
can be tied to V
IN
or some other voltage source. If the BIAS
pin voltage is too high, the efficiency of the LTM8050 may
suffer. The optimum BIAS voltage is dependent upon many
factors, such as load current, input voltage, output voltage
and switching frequency, but 4V to 5V works well in many
applications. In all cases, ensure that the maximum voltage
at the BIAS pin is less than 25V and that the sum of V
IN
and BIAS is less than 72V. If BIAS power is applied from
a remote or noisy voltage source, it may be necessary to
apply a decoupling capacitor locally to the pin.
Load Sharing
Tw o or more LTM8050’s may be paralleled to produce
higher currents. To do this, tie the V
IN
, FB, V
OUT
and SHARE
pins of all the paralleled LTM8050’s together. To ensure
that paralleled modules start up together, the RUN/SS pins
may be tied together, as well. If the RUN/SS pins are not
tied together, make sure that the same valued soft-start
capacitors are used for each module. Current sharing
can be improved by synchronizing the LTM8050s. An
example of two
LTM8050s configured for load sharing is
given
in the Typical Applications section. When n number
of units are connected for parallel operation and a single
feedback resistor is used for all of them, the equation for
the feedback resistor is:
R
FB
=
394.21
N V
OUT
– 0.79
( )
kΩ
Burst Mode Operation
To enhance efficiency at light loads, the LTM8050 auto-
matically switches
to Burst Mode operation which keeps
the output capacitor charged to the proper voltage while
minimizing the input quiescent current. During Burst Mode
operation, the LTM8050 delivers single cycle bursts of
current to the output capacitor followed by sleep periods
where the output power is delivered to the load by the output
capacitor. In addition, V
IN
and BIAS quiescent currents are
each reduced to microamps during the sleep time. As the
load current decreases towards a no load condition, the
percentage of time that the LTM8050 operates in sleep
mode increases and the average input current is greatly
reduced, resulting in higher efficiency.
Burst Mode operation is enabled by tying SYNC to GND.
To disable Burst Mode operation, tie SYNC to a stable
voltage above 0.7V. Do not leave the SYNC pin floating.
LTM8050
15
8050fc
For more information www.linear.com/LTM8050
APPLICATIONS INFORMATION
Figure 1. Apply an RC Network to RUN/SS to Control the
Soft-Start Behavior of the LTM8050 at Power-Up
Minimum Input Voltage
The LTM8050 is a step-down converter, so a minimum
amount of headroom is required to keep the output in
regulation. In addition, the input voltage required to turn
on is higher than that required to run, and depends upon
whether the RUN/SS is used. As shown in the Typical
Performance Characteristics section, the minimum input
voltage to run a 3.3V output at light load is only about 3.6V,
but, if RUN/SS is pulled up to V
IN
, it takes 5.5V
IN
to start.
If the LTM8050 is enabled with the RUN/SS pin after V
IN
is applied, the minimum voltage to start at light loads is
lower, about 4.3V. Similar curves detailing this behavior
of the LTM8050 for other outputs are also included in the
Typical Performance Characteristics section.
Soft-Start
The RUN/SS pin can be used to soft-start the LTM8050,
reducing the maximum input current during start-up. The
RUN/SS pin is driven through an external RC network to
create a voltage ramp at this pin. (See Figure 1).
By choos-
ing an appropriate RC time constant, the peak start-up
current
can be reduced to the current that is required to
regulate the output, with no overshoot. Choose the value
of the resistor so that it can supply at least 20μA when
the RUN/SS pin reaches 2.5V. Output voltage soft-start
waveforms for various values of R
SS
and C
SS
are given in
the Typical Performance Characteristics section.
RUN/SS
RUN
RUN
100k
C
SS
This in turn limits the amount of energy that can be delivered
to the load under fault. During the start-up time, frequency
foldback is also active to limit the energy delivered to the
potentially large output capacitance of the load.
Synchronization
The internal oscillator of the LTM8050 can be synchronized
by applying an external 250kHz to 2MHz clock to the SYNC
pin. Do not leave this pin floating. When synchronizing
the LTM8050, select an R
T
resistor value that corresponds
to an operating frequency 20% lower than the intended
synchronization frequency (see the Frequency Selection
section).
In addition to synchronization, the SYNC pin controls Burst
Mode behavior. If the SYNC pin is driven by an external
clock, or pulled up above 0.7V, the LTM8050 will not
enter Burst Mode operation, but will instead skip pulses
to maintain regulation instead.
Shorted Input Protection
Care needs to be taken in systems where the output will
be held high when the input to the LTM8050 is absent.
This may occur in battery charging applications or in
battery backup systems where a battery or some other
supply is diode ORed with the LTM8050’s output. If the
V
IN
pin is allowed to float and the SHDN pin is held high
(either by a logic signal or because it is tied to V
IN
), then
the LTM8050’s internal circuitry will pull its quiescent
current through its internal power switch. This is fine if
your system can tolerate a few milliamps in this state. If
you ground the RUN/SS pin, the input current will drop
to essentially zero. However, if the V
IN
pin is grounded
while the output is held high, then parasitic diodes inside
the LTM8050 can pull large currents from the output
through the V
IN
pin. Figure 2 shows a circuit that will run
only when the input voltage is present and that protects
against a shorted or reversed input.
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8050. The LTM8050 is neverthe
-
less a switching power supply, and care must be taken to
Frequency Foldback
The
LTM8050 is equipped with frequency foldback which
acts to reduce the thermal and energy stress on the internal
power elements during a short circuit or output overload
condition. If the LTM8050 detects that the output has
fallen
out
of regulation, the switching frequency is reduced as a
function of how far the output is below the target voltage.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24

LTM8050MPY

Mfr. #:
Buy LTM8050MPY
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators [Tin-Lead SnPb BGA] 58V, 2A Step-Down Module Regulator
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